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February 20, 2009

Honest Crabs, Power To The Hungry, Nice Mice And Clever Meerkats

by Sam Savage

An article by Princeton Biologist Mark Laidre suggests that when an animal signals an intent to attack, chances are it's not bluffing. Using hermit crabs as subjects, Laidre tested previous mathematical models that predict animals have a significant incentive to give dishonest signals about their intentions. Some models suggest that animals may lie about their intentions up to 40 percent of the time. Laidre used dummy hermit crabs to invade the personal space of live crabs. Contrary to the models, the crabs nearly always backed up their threats with an attack. Those that didn't signal a threat nearly always fled. The findings, Lairde says, suggest that animals don't lie about their actions nearly as much as theorists once predicted.

Mark E. Laidre, "How Often Do Animals Lie About Their Intentions? An Experimental Test," 173:March.

POWER TO THE HUNGRY: HOW THE NEEDIEST CAN LEAD LARGE GROUPS

Flocks of birds, swarms of insects and herds of ungulates don't need to take a vote to choose their leaders. According to research led by Larissa Conradt (University of Sussex), leaders in large animal groups can emerge automatically. Conradt and her colleagues created a theoretical model that simulates the movements of a large group in which members have conflicting plans about where they'd like to go. The simulation showed that individuals who valued their preferred destination over group cohesion often led the group"”even if they were in the minority. Those who were less concerned about the destination went along for ride just to stay with the group. "As a consequence," Conradt says, "large groups are often automatically led by those members that are most desperate to reach a particular destination, or are most indifferent as to whether or not the group breaks up." There's some empirical evidence to back up the model. Studies have shown that food deprived fish move to the front of shoals, presumably to steer the group toward food.

Sometimes the nice guy gets the girls. At least that's how it is for striped mice. A research team led by Carsten Schradin (University of Zurich and University of the Witwatersrand) studied the breeding strategies of striped mice in South Africa. They found that dominant males who controlled breeding groups had lower testosterone levels than subdominant males. "What is unusual about this society is that the dominant males are in fact the most sociable, often grooming other group members," Schradin says. "It is the smaller and solitary living males, which roam from one group to another, that have the highest testosterone levels." The roaming males try to coerce females to mate, which, as one might imagine, is less successful than establishing a breeding group.

Meerkats' cooperative social structure may have led them to evolve a specialized system of alarm calls, according to an article by Roman Furrer and Marta Manser from the University of Zurich. Meerkats have the ability to vary their alarm calls depending on what type of predator threatens them. In other words, they use one call when threatened from the air by an eagle, and a different call when threatened from the ground by a snake. But Cape ground squirrels, that live side-by-side in the same habitat as meerkats, have not evolved this type of alarm call. So why would such calls evolve on one species and not the other when both live in the same area? Furrer and Manser suggest it has to do with social structure. Meerkats are highly social creatures. They coordinate their foraging activities as well as their escape plans. So knowing what predator is approaching helps in coordination. The ground squirrels, on the other hand, act largely independent of each other and may have less need for specified alarm calls.